1. Field of the Invention
The present invention relates to a method for manufacturing a clutch housing used for an automatic transmission of a vehicle or the like.
2. Description of the Related Art
A drum-type clutch housing is generally used for an automatic transmission (AT) of an automobile or the like. Such a clutch housing is manufactured to have predetermined accuracy and dimensions with a cold forging technique.
The clutch housing usually comprises a central shaft portion and an outer drum portion coupled thereto. The shaft portion and the outer drum portion are firmly coupled by welding, fastening and the like.
Such a manufacturing method is also known wherein the clutch housing is previously hot-forged into a product shape, and then predetermined accuracy is secured through cold forging, as disclosed in Japanese Patent Application Laid-open No. 3-189044 (“Patent document 1”), for example. In this example, the shaft portion and the outer drum portion are integrally formed.
The clutch housing described above has the following problems.
In the conventional clutch housing, the outer drum portion with a spline provided on its inner periphery and the shaft portion are processed from separate members, and then integrally jointed by welding, fastening or the like. This makes it easy to form oil holes and notches in the shaft portion, but at the same time poses problems of decreased strength and accuracy of a joint portion.
In order to solve the problems in manufacturing by coupling separate members, it is necessary to form integrally by forging as described in Patent document 1, for example. Such integral forming allows improvement in strength and accuracy as compared with a method in which the outer drum portion and the shaft portion are configured from the separate members and coupled, but leaves a problem that it is difficult to form the oil holes and notches in desired shapes in the shaft portion.
Since the outer drum portion obstructs entry of a drilling tool or the like into the shaft portion, the oil hole to be pierced in the shaft portion can not be pierced vertically to a shaft center and is thus pierced obliquely. When it is obliquely pierced, a boring machine such as a drill cannot be precisely positioned at the shaft portion, resulting in another problem that the oil hole cannot be pierced exactly at a predetermined position. A similar problem also occurs in a process of forming a notch such as a groove provided in the shaft portion.